In my teenage punk rock band days, I borrowed my friend's "old" bass amp for some gigs - a vintage mid 60's black panel Fender Bassman head - and ran it through my Marshall 4x12. I was annoyed because I couldn't get it to stay clean when I cranked it up. Oh man I'd love to go back in time and play through that thing properly with fresh ears.
Later on in another punk band, we gigged a THD Univalve into an Avatar 4x12 with V30's. Amp was basically turned up full tilt with a boost pedal. I forgot about this until recently but we actually blew the amp and had to get it fixed. Turns out you don't want to run amps on 10 forever.
Didn't get it this way but one time I turned my friend's DSL100 full blast through the matching 4x12. That thing was crushing with massive feedback. I think I had to go stand in another room with the doors shut and earplugs in to be able to do that.